Semiconductor substrates are widely used for fabricating a variety of semiconductor-based components and devices including electronic devices, microelectromechanical devices, and opto-microelectronic devices. Better measuring and characterizing substrate properties can improve the yield and the performance of semiconductor devices and circuits. Substrate characterization can be further used to facilitate research and development in semiconductor substrate materials and devices.
One critical area of semiconductor characterization is substrate evaluation and specification of substrate absolute thickness, thickness uniformity, or micro features formed in a substrate. Such information is essential to failure analysis and evaluation of device performance. There has been continuous effort in developing various reliable and fast techniques of substrate characterization, especially, nondestructive measuring techniques and systems that can work with ultra-thin wafers (e.g., 1 .mu.m.about.100 .mu.m in thickness).